Music for speaker setup?

I am getting serious about positioning my speakers. I have a small, irregularly shaped room and small changes in placement can result in significant changes to sound.

It would be very helpful if I had a few recordings that were "known quantities" as far as imaging. What happens is that I get the speakers positioned where they seem to work well with some recordings, then I put on another disk and hear something I don't expect (off-center soloist, for instance). But you never know; maybe in this particular recording the soloist is supposed to be off-center. In classical and many jazz recordings, the engineers aim to reproduce the sound of the actual performance, so a photo or description of how the performers were arranged would help. Pop recordings are full of various effects, but knowing that on track X the guitar is supposed to be far to the left, or whatever, would be good. If I had a few such references I'd feel more confident in my results. Any suggestions for recordings that provide this kind of information?

Thanks for any help.